1. Field of the Invention
The present invention relates to a microfluidic device for circulating liquid. To be more precise, the present invention relates to the use of a liquid circuit in a small device for use in the fields of chemistry, biology, biochemistry, and medicine.
2. Description of Related Art
Microfluidic systems of this type have been used increasingly in recent times because, given their small size, they require the use of only limited volumes of liquid, which has a number of advantages. This type of small equipment is relatively easy to mass produce at limited cost, incorporates a number of functions within a small overall size, and is highly reliable. In particular, for carrying out analyses by means of a reaction, these small devices offer high sensitivity and fast analysis and are easily transportable.
Microfluidic devices that achieve these objectives have been produced using techniques and materials that are conventionally used in the semiconductor industry. There is a need for microfluidic devices of this kind for more widespread use, with liquid circulation paths that are not totally predefined in advance, so that the liquid circulation paths can be finalized by the user from a number of options. Such modularity means that the same microfluidic device addresses multiple demands.
The document WO2004/050242 proposes a microfluidic device using a stack of plates for creating one of a number of microfluidic networks on demand, by means of an external command. To provide fluid communication between two cavities or passages, the wall between them is pierced by targeted electromagnetic radiation. Centrifugal force is applied to the liquid to move it.
Techniques of that type have a number of drawbacks, however. External means are necessary for rotating the microfluidic device to generate the centrifugal force, which greatly complicates implementation. Also, a centrifugal force can move the liquid in only one direction.
Activatable materials exist of volume that can be locally varied, in particular increased, upon activation, in particular thermal activation.
See for example B. Sämel, P. Griss, G. Stemme, “Expandable microspheres incorporated in a PDMS matrix: a novel thermal composite actuator for liquid handling in microfluidic applications”, Transducers '03, 1558-1561 (2003), which demonstrates the possibility of filling small voids or larger reservoirs in a microfluidic device by using in the stack a layer formed of a composite material resulting from mixing a polymer, in particular polydimethylsiloxane (PDMS), or silicone, with expandable microspheres, in particular Expancel™ microspheres. In the present patent application this mixture of polydimethylsiloxane and Expancel™ microspheres is referred to as XBPDMS.
An object of the present invention is to propose a microfluidic device offering multiple options for forming three-dimensional liquid networks consisting of passages and/or valves and/or cavities. The microfluidic device can therefore be a device that is standard in terms of its fabrication, the end user being able to choose between the above-mentioned options, according to requirements, by activating one or more areas of an activatable material present in the device in one or more steps.
The expression “three-dimensional liquid network” refers to a liquid path at different heights within the stack forming the device, which increases the number of liquid paths used simultaneously without increasing the size of the device, which paths can cross without communicating with one another because they cross at different heights, and in particular in different layers of the stack.